Purification and characterization of chemical analytes such as polypeptides, polynucleotides, and polysaccharides, have become increasingly important in the chemical and medical arts. Numerous analytical methods have been developed for a variety of purposes, such as testing for the presence of biological contaminants or toxins, identifying new components in biological systems, and verifying sample purity, for example. Often, analytes of interest are available only in trace amounts or at very low concentrations. Accordingly, there has been much interest in developing analytical techniques with increased sensitivity to facilitate characterization of such analytes.
For many applications, one or more purification steps are necessary before the analyte(s) of interest can be detected or quantified. In the case of analytes which are present in trace amounts, purification has proved difficult for a number of reasons. For example, when analytes elute closely together under given separation conditions, it has been difficult to collect adjacent peaks in a manner that retains resolution, i.e., without significantly diminishing the resolution achieved by the selected purification method. Such small-sample purifications have also been hampered by low sample recoveries due to dilution or adherence of sample on collection vessel surfaces.
Although fraction collection using individual collection vessels has been the traditional mode for collecting and storing resolved sample components, this approach has generally been unsuitable for small sample amounts because of low recoveries as above. Accordingly, other collection methods have been proposed.
One proposed approach involves collecting eluted samples on an adsorbent surface by continuously dragging the outlet of a chromatography column across an adsorbent surface, such that the column effluent is continuously dispensed onto the adsorbent in a continuous trail. Such a method has been proposed by Murata et al. (1993) for collecting polypeptides from a capillary liquid chromatography column. In their method, a pen-holding device is used to maintain the column outlet in continuous contact with a collection membrane.
Although such dragging methods have allowed relatively simple apparatus design, subsequent experience has shown that the fluid outlet often snags on the adsorbent surface, leading to tearing or gouging of the surface or, conversely, locking of the outlet onto the surface so that the outlet cannot move or the adsorbent moves with the outlet. Temporary catching of the outlet on the membrane can lead to discontinuities and other irregularities in the deposited sample, so that the locations of resolved peaks do not correspond with the true elution profile. Tearing or gouging can seriously hinder sample recovery. Long-term locking between the surface and the outlet can result in superimposition of some or all of the resolved peaks, defeating the purpose of the separation. Yet another drawback of the dragging method is the possibility of cross-contamination of eluate due to carry-over of liquid between the capillary outlet and the adsorbent collection layer.
It would be desirable to provide an apparatus and method for collecting small amounts of eluted sample components with high sample recovery, while avoiding the problems mentioned above. In particular, it would be desirable to provide such a method for collecting separated sample components in a manner that allows immediate use or long-term storage for subsequent analysis.